Signaling



1929. J. F. FARRINGTON 1,738,235

SIGNALING Filed Sept. 27. 1919 4 Sheets-Sheet 1 John F Q/n /hg/Oh by 636%M7M my Dec. 3, 1929. J. F. FARRINGTON 1,738,235

SIGNALING Filed Sept. 2'7. 1919 4 Sheets-Sheet 2 game FlL zFr I Deg. 3, 1929. J. F. FARRINGTON 1,738,235 SIGNALING Filed Sept. 27. 1919 4 Sheets-Sheet 3 f7 fs? bye/270m J hn F Far? vhgfan Dec. 3, 1929. J. F. FARRINGTQN 3 SIGNALING Filed Sept. 27. 1919 4 Sheets-Sheet 4 -1.... m f/idl 7 fiz dz f7i-35 y FZ-Y/W Patented Dec. 3, 1929 UNITE STATES PATENT OFFICE JOHN F. FARRINGTON, OF NEW YORK, N. Y., ASSIGNOR TO WESTERN ELECTRIC GOD/L PANY, INCORPORATED, OF NEW YORK, N. Y., A CORPORATION OF NEW YORK SIGNALING Application filed September 27, 1919. Serial No. 326,986.

This invention relates to signaling systems and as illustrated in the embodiments herein described, is particularly adapted for use in radio telephone systems.

Duplex working of radio or other high frequency systems has previously been a matter of some diiiiculty because of the excessive influence of the local transmitter upon the local receiver at each station.

It has often been the practice in designing radio systems, to provide a switch for switching an antenna system from a transmitting to a receiving set so that transmission and reception could be carried on alternately. It has also been suggested to provide a transmitter connected to an antenna system so as to be in conjugate relation to a receiving system likewise connected thereto, whereby a minimum amount of the transmitted energy is impressed upon the receiving set. In accord ance with the principles of this invention, however, it is not attempted to completely prevent the energy of the outgoing carrier frequency from acting upon the local receiver. A certain amount of energy of the outgoing carrier frequency is utilized in the receiving set. This causes amplification of the received signals and also produces a side-tone effect similar to that in an ordinary telephone substation. The loudness of the outgoing signals or the effect thereof upon the local indicating instrument, will generally be of approximately the same degree of magnitude as that of the incoming signals.

These results are accomplished by causing the received energy and a certain amount of energy of the outgoing carrier frequency to be combined and detected, thereby producing a local auxiliary carrier current Wave. This auxiliary carrier frequency current Will be modulated or varied in amplitude in accord ance with both the outgoing and the incoming signals and by detecting it a Wave will be produced from which may be derived both the incoming and the outgoing signals. The

auxiliary carrier frequency may be either equal to the sum or the difference of the principal carrier frequencies, but since many practical advantages are attached to using the difference frequency rather than the sum frequency, this is the one which may most conveniently be utilized. It should be noted however, that the sum frequency may be used as the auxiliary carrier frequency although the selectivity will not be as great. The amplitude of the auxiliary carrier frequency will be proportional to the product of the amplitudes of the local and the distant carriers. Thus, assuming the same percentage of modulation at each station, the signal heard in the local receiver will be of approxi mately the same intensity whether the local or distant station is transmitting. In order to obtain a maximum indication from the dis tant station, it is consequently desirable to allow suflicient energy of the local carrier wave frequency to enter the receiving circuit to load the detector or the detecting device with approximately the maximum energy in put which itis capable of handling Without distortion. The local energy is thus utilized as a desirable amplifying and selecting agent during the non signaling periods.

The object of the invention, broadly stated, is, therefore, to provide improved methods of and means for duplex signaling, and more specifically for radio signaling.

A further object is to provide a duplex system wherein the locally generated carrier wave for the outgoing signals aids in selecting and amplifying the incoming signals. The effects of interfering Waves on radio systems are thereby to a considerable extent overcome.

A further object is to provide a system in which the transmitting operator will at once become cognizant of an inoperative condition of his transmitting or receiving system or that of the distant transmitter. The absence of side tone effect will Warn the operator that the apparatus is not working properly.

Another object is to provide systems utilizing the principles herein described and adapted for multiplex receiving. While transn'iitting, one message or a plurality of messages from two or more separate stations may be received without any change in the apparatus. The operator at either of the other stations may likewise transmit and receive from each of the communicating stations. Such a system corresponds in a man-- ner to the ordinary party line in ordinary telephony whereby each of three or more persons may talk and all the others may listen.

Among the further objects of the invention which will be apparent to those skilled in the art, from a perusal of the following detailed description, is that of providing efficient and simple forms of apparatus for carrying the prineiplesof the invention into effect.

In comiection with the detailed description, reference will be made to the accompanying drawings wherein Figs. 1 to i in-- elusive each illustrates one of the two sta-- tions of a duplex system whereby a single telephone conversation may be carried on; Fig. 5 is a modified form of the antennatuningmeans adapted for use in F ig. 3; Fig. 5 illustrates a modified form of system in which either or all of two or more messages may be received during or alternately with the transmission of a single message; Fig. 5 is a modified form of filter adapted for use in connection with Fig. 5 or other similar systems; Figs. 6 and 7 are still other forms of systems of which Fig. 6 is adapted to receive two messages at one time, and Fig. 7 a single message only; Fig. 8 illustrates the principles of the invention as applied to a station having separate transmitting and receiving antenna; Fig. 9 illustrates a form of system in which an additional locally generated auxiliary frequency current is used for the purpose of securing greater selectivity; and Fig. 10 illustrates a form of station which may be utilized for the reception of a plurality of individual messages arriving from one ormore stations while another message is being transmitted.

Referring specifically to Fig. 1, the outgoing speechsignal waves 8 from the microphone circuit 1, are impressed with a high frequency carrier wave f from the source 2 which, for 'example,'may be of a frequency of'500,000'cyoles per second, on the input circuit of a modulating tube or other equivalent modulator 3. A wave of frequency modulated'byspeech s is thereby produced in the output circuit 4 and impressed by means of the'transformer 5 upon the amplifier 6, which is'preferably of the thermionic type. The

output circuit of the amplifier 6 includes a circuit "A which is preferably tuned to the mean ofthe current of freqency f modulated byspeech'waves 8 This modulated current is herein designated by the expression f is This symbolic manner of designating a modulated'wave will be used throughout this specification. A circuit B is tuned to the frequency f which isthe'mean frequency of theoutgoingmodul-ated wave f :8 in order to preventt-theoutgoing waves which are impressed upon the antenna 7 from being shunted toa material extent through the shunt circuit8 inwhich the circuit B is placed. Any

- of the condenser 17.

suitable reactance means 9, such as in the present instance a coil 10 shunted by a condenser 11, is provided in the shunt branch 8 as a tuning reactance to give the antenna system a degree of freedom equal to the mean of the incoming waves f is which represent the modulated wave received from a communicating station. A tuned circuit C is provided in the output circuit of the amplifier 6. This circuit is tuned to a frequency equal to the difference between the frequencies f and f Thus, if frequency f equals 500,000 and f equals 580,000, circuit C will be adjusted to be resonant at 30,000 cycles. Owing to the detecting action of the amplifying tube 6 which has its anode-cathode circuit in series with circuit C, there will occur in circuit C oscillations having a component with a frequency of 80,000 cycles and modulated in ac cordance with the speech signal 8 or the signal 8 or by both of them in case both are being simultaneously transmitted. This is represented by the legend fi-fiitii adjacent the circuit C. A circuit D tuned to the same frequency as the circuit C, is coupled thereto, preferably loosely. The circuit D is serially included in the input circuit of a hermionic or other suitable detector 12, whose output circuit includes a telephone receiver 13, shunted by condenser 14, or any other suitable indicating device.

Operation of Fig. 1.-The greater part of the high frequency energy which is being transmitted will not affect the circuit D but will pass through the circuit C without producing much effect in circuit D. That part of the unmodulated outgoing energy which is impressed upon the circuit C will perform the useful purpose of aiding in the selective reception and amplification of the incoming signal. Since the amplitude of the auxiliary or intermediate frequency impressed upon the detector 1.2 will have a value dependent on the amplitudes of the carrier frequencies of the two stations, the signal heard in the local receiver will consist of both the local and the distant signal and these will be of the same order of loudness. The legend s 5 adjacent the receiver 13 indicates that both signals will be heard in this instrument. The use of the letters 7" and s with appropriate subscripts are applied to the remaining figures of the drawing with meanings similar to those in connection with Fig. 1.

The transmitting system shown in Fig. 2 comprises an antenna 7 to which is connected a vacuum tube in L1 \VGll-kDOWD 11121111161 as illustrated, whereby oscillations are produced in the antenna at a frequency approximatelyequal to the natural frequency determined by the series arrangement comprising the capacity of the radiating member, the inductance of the coil 16, and the capacity Space current for the be in'ipressed upon the antenna 7.

tube 15 is provided by the source 18, through the speech frequency choke coil 19, the circuit 20, and the high frequency choke coil 21. The choke coil 21 functions to discriminate against both the incoming and outgoing high frequency waves. and therefore tends to lreep them out of the circuit 20. Shunted around the source 18 and the coil is the anode-cathode path of the vacuum tube 22. The input circuit 23 of the tube 22 is coupled to the microphone circuit 2a which represents any suitable source of speech or other signaling frequency electrical waves or variations. The production of speech waves in the circuit 2% will cause a corresp riding variation in the impedance of the tube 22, which will in turn cause a corresponding variation in the current supplied to the tube owing to the choking action of the coil 19. This will cause the high frequency wares generated in the antenna by the oscillating tube 15 to vary in amplitude in accordance with the waves produced in the circuit 24. Incoming signal waves will Owing to the detecting action of the tube 15 upon both incoming and outgoing high frequency waves a variation of potential difference will be produced across the anode and the cathode of the tube 5 of a frequency equal to the difference between the carrier frequencies. The tuned circuit will be adjusted to be resonant to this difference frequency. In solecting the modulated auxiliary carrier frequency wave the circuit functions in the same manner as the circuit designated C in Fig. 1 and other figures. A circuit comprising a variable condenser and a variable inductance may be connected in parallel to the circuit containing the source 18 and the coil 19. The circuit 25 may be most advantageously tuned to be resonant at the auxiliary carrier frequency. This prevents a loss of energy of the auxiliary carrier fre quency due to the voltage drop across the tube 22. Coupled to the circuit 20 is the circuit D which tuned to the auxiliary carrier frequency. The circuit D is in the input circuit of the detector 12 in the output circuit of which is the receiver 13. The branch circuit 8 which is connected to the antenna, is intended to give the antenna one natural period equal to the period of incoming waves from the distant station which are represented by the legend f is An anti-reson ant B is serially included in the branch 8 and tuned to the transmitting carrier frequency f, in order to prevent current of that frequency from passing through the branch 8. Any suitable tuning means 10 is also provided in the branch 8 whereby the said branch may be given any desired reactance which is necessary to tune the antenna for the incoming waves. An important feature of this arrangement is that the frequency of the waves being transmitted is determined by and can be varied by the adjustment of the coil 16 and the condenser 17. After establishing the outgoing carrier at the desired frequency, the tuning reactance means may be varied within considerable limits without producing a material variation of the waves being generated by the tube 15 in the antenna.

wmtimt of Fig. flr- When signals are being transmitted there will be radiated from the antenna 7 a modulated carrier wave 7 's When no signals are being transmitted the carrier wave f is available for combination with the incoming signaling wave f is which causes the transmission through circuits 20 and D of the wave frflitleither or both of the signals 5 and 8 de pending on whether one or both are that instant being transmitted. When transmission is going on, of course, only the unmodulated component of the outgoing carrier combines with the incoming wave to effect amplification thereof.

In 3 the circuit T represents any suitable system for generating modulated waves and transmitting the modulated waves as an outgoing signal by impressing the waves upon the antenna system 7 and thereby causing their radiation thereform. If the transmitting carrier frequency f is 500,000 then the circuit B will be adjusted to resonance at that frequency in order to prevent the dissipation of transmitted energy in the branch circuit 8. The incoming modulated carrier wave f e: is impressed upon the circuit A. Suitable tuning reactance means 0, such as coil 10 and condenser 11, are provided to tune the antenna for the incoming frequency. The circuit A is tuned to the incoming carrier f but sufficient of the outgoing carrier 7', will be impressed upon this circuit so that the combined waves, when detected by the detector 26, will produce current of the auxiliary carrier frequency, which is equal to the difference of the two principal frequencies, in the tuned circuit C to w rich is coupled the circuit 1), circuits C and D being resonant at the frequency of the auxiliary carrier. The detector 12 and the receiver 13 are similar to those described in the preceding figures. The operation of this system will be understood from a consideration of the descrip tion of the operation of the preceding arrangements'.

Figure 3 represents a form of circuit which may be substituted for that portion of Fig. 3 between the dotted lines X and X. The tuning means here consists of elements arranged and functioning similarly to the coil 10 and condenser 11 in Fig. 1. The circuit A which is coupled thereto has the same tuning as in Fig. 3.

Fig. 4 comprises a system in which the ele- This produces in the receiver 13 ments 7,16, 17 15, 18,19, 20,21, 22, 23, 24, 12, 13, 14 and D are similar to and function in the same way as the corresponding elements in Fig. 2. The antenna, in the arrangement ofthis figure, is tuned only for the outgoing signals hence the incoming signals will be received rather inefficiently. However, a shunt circuit 8 containing elements similar to the circuit 8 of Fig. 2 may be provided if desired. In Fig. 2 it will be noted that the voltage of speech or signaling frequency which is supplied to the oscillating tube 15 from the tube 22 is impressed serially across the circuit 20. In some cases this results in objectionable transients being set up in circuit 20 which cause interference with the operation of the system. In order to avoid this in the arrangement of Fig. 1, the circuit 20--is balanced for speech frequencies. The lead from the plate of the tube 22 is connected to an intermediate point 27 of the coil 28 and balancing reactance means 29 which may be of any suitable form, is provided. This reactance means is so adjusted that the time constant of the circuit from the point 27 through the oscillator 15 to ground is R of the circuit from the point 27 through the network 29, which may be designated an oscillator simulating impedance, to ground. This is called an oscillator simulating impedance because it is so designed as to simulate, at mean speech frequency, the impedance of the oscillating tube 15 and its associated circuit. The circuit 25, as shown in Fig. 2, has been omitted in Fig-4, but may be provided if desired. The leak path 30 of the oscillator 15 comprises an inductance in series with a parallel combination of a resistance and a condenser. The currents of the intermediate carrier frequency in the circuit D, instead of being impressed directly upon the detector 12, are first amplified by means of a suitable amplifying device 31 and then passed through any suitable filter 32 to the detector 12. The filter 32 is designed to pass only modulatequal to the time constant 5 ed auxiliary carrier frequencies, 7 f i 2 This arrangement of amplifier and filter, although shown only in connection with Fig. 4, is equally well adapted for use in connection with arrangements shown in any of the other figures. The general operation of this system will be readily understood from a pcrusal of the description of the operation of the system shown in Fi 2. Balancing the circuit 20 for speech frequencies will reduce the amplitude and number of disturbing transients set up therein.

1 Fig. 5 illustrates another application of the invention with additional features whereby the system is adapted to receive'two or more messages either simultaneously or successively without the operation of switches or any other change in the circuit arrangement. The transmitting circuit T comprises any suitable source 2 of carrier waves of frequency f and any suitable source of signaling waves 8 such as a microphone circuit 1. These waves are impressed upon the modulator 3. The modulated waves are impressed upon the amplifier 6, the output circuit of which is coupled to an antenna system 7 by means of a branch circuit 33. The antenna circuit 7 comprises the usual radiating means, a circuit 34 which is used for tuning to the mean of the incoming waves which are to be received, and a balancing network N which consists of any suitable reactance elements 35. This particular form of network and general arrangement for obtaining a balance are the invention of another and are herein claimed only as a part of the invention outlined. The branch circuit 33 is connected to an intermediate point of the coil 36 in the circuit 34 so that there will be impressed upon the circuit A a minimum amount of energy of the outgoing carrier frequency. The reactance of the network N is so adjusted that only a small amount of energy of the outgoing carrier frequency is impressed upon circuit A. The circuit A is tuned, however. to the mean of the incoming frequencies so that the maximum amount of incoming energy will be received therein. The detector 26 includes circuit A in its input circuit and has in its output circuit a suitable number of circuits C and C to which are coupled respectively a suitable set of circuits D and D. Each pair of circuits C, D and C. D are tuned as hereafter described. Each circuit D will feed into a suitable detector 12 in the output circuit of which is located a receiver 13.

Operation 0 Fig. 5.Suppose in this system it is desired to transmit signals on a car rier wave having a frequency f equal to 500,000 cycles per second. and to receive from one or more other stations two signals on carrier waves having frequencies of 510.000 and 520,000 cycles per second; then the first auxiliary carrier frequency will be 10,000 cycles and the circuits C and D will be tuned to select this frequency. The second auxiliary carrier will have a frequency of 20,000 cycles and the circuits C and D will be tuned to select this frequency. Additional selective circuits may be provided to selectively receive additional signals if desired.

7 Fig. 5 shows an optional form of selective circuits in the form of band filters which may he used in place of the circuits C, D and C. D, as included between the lines X, X in Fig. 5. Obviously since circuits C and D function similarly in all of the described species of the invention the circuits X, X may be substituted for the circuits C. D of any figure. The band filter B7 will be adjusted to select one modulated auxiliary carrier frequency to the exclusion of all other currents and the band filter Bf is similarly adjusted to transmit another auxiliary carrier frequency, etc. Reference is made to the patent of Campbell No. 1,227 ,113, granted May 22, 1917 for a full description of the method of designing band filters of the hind illustrated, to pass any desired range of frequencies. The information given in the said patent will enable any one skilled in the art to construct filters having the constants necessary to enable them to function for the purpose and in systems of the kind herein described.

Referring to Fig. 6, it will be seen that the transmitting system T is similar to the transmitting system illustrated in Fig. 2. The receiving system, however, is associated with the transmitting system in a different manner and hence only so much description of the transmitting system will be given as is necessary to understand the relation of the receiving system with respect thereto. The tuned circuit 20 and the circuit are omitted from the system of Fig. 6. In order to accomplish .wreception there is connected to the tuning reactance means 10 a suitable circuit A which is broadly tuned to the mean of the incoming frequencies. The circuit A is included in the input circuit of a detector 26. The circuits and apparatus connected to the output circuit of the detector 26 are similar in function to those circuits and apparatus connected to the output circuit of the detector 26, in Fig. 5, hence no detailed description thereof need be given.

In the operation of this system the oscillating tube 15 produces in the antenna circuit 7, carrier waves of frequency 7, which are modulated in accordance with signaling variations produced in the microphone circuit 24:. In order to prevent the outgoing waves from being shunted through the branch 8, the circuit B is provided which is tuned to the frequency f The incoming waves as represented by the legends 721-8 and fg g are received by the antenna and cause an effect in the receivers 13 each with its appropriate signal in a manner heretofore described in connection with Fig. 5.

The circuit arrangement of Fig. 7 is substantially identical with that of Fi 6, the only difference being that the leak paths of the high frequency oscillators are different in the two circuits and that the circuit of Fig. 7 is intended to receive only a single signal, hence only a single set of tuned circuits C, D is provided.

Fig. 8 illustrates the application of the invention to a system having separate transmitting and receiving antennm. The transmission system is conventionally represented by the microphone circuit 1, the modulator 3 and the source 2 of high frequency waves. This typifies any suitable system for impressing high frequency modulated waves upon the antenna 7 The receiving system comprises an antenna circuit 7 tuned to be selective of waves of the frequency transmitted from a distant communicating station T. A circuit- A which is tuned to the same frequency is coupled to the antenna 7. The circuit it typifies any desired means for discriminatin against the locally transmitted waves in favor of the received waves from a distant communicating station. The detector 26, circults G and D, the detector 12, and the receiver 13 function in a manner similar to the corresponding elements described in connection with Fig. 3. The waves from the distant transmitter T" are received upon the antenna 7 together with waves from the local transmitter T. A system of this sort is more desirable than those having a single antenna when the amount of locally-generated highfrequency energy received from the local transmitter is proportionally large. The antennae 7 and 7 may be of any desired form and may have any desired special relation and be any suitable distance apart. Thus if station T were 1000 miles from the antenna 7 the antenna 7 might, as an extreme example, be located 50 miles from antenna 7. The circuit 37 would connect the transmitting microphone with the antenna 7, the microphone and the receiver 13 forming a single operators sub-set.

In the arrangement of Fig. 9, provision is made for greater selectivity by utilizing an additional local auxiliary source 36. Suppose for example the frequency f is 1,000,000 cycles and the frequency is 1,200,000 cycles, then the beat frequency to which the circuits C and D are tuned will be 200,000 cycles. If the circuits C and D are not sufficiently selective to discriminate between 190,000, 200,- 000 and 210,000 cycles satisfactorily, in order to prevent interference by the stations operating 10,000 cycles above or 10,000 cycles below the principal carrier frequencies, then the local generator 36, having a frequency of for example 220,000 cycles, is provided to feed energy into the circuit D. Then in the output circuit of the detector 37 will be a component having a frequency of 20,000 cycles which could be selectively separated from frequencies of 10,000 or 80,000 cycles which the interfering waves would produce. The circuits H and J would, therefore, be tuned to be resonant at 20,000 cycles. In the output circuit of the detector 12 the desired 1 signal will be produced. Since the auxiliary carrier wave produced in and transmitted through circuits H and J is a modulated wave resulting from the combination of three other waves, namely those having frequencies 7",, and f it is represented by the legend fljffsilii' In Fig. 10 is illustrated one station of a system in which results may be secured by wireless similar to those obtained on a partyline telephone system. From a suitable transmitting station'T the modulated high frequency waves f s are impressed upon the antenna 7. The circuit B is adjusted to allow only a small amount of this current to pass/through the shunt branch 8. A plurality of modulated waves from other stations represented by fii's f ir etc, may be received by the antenna 7 The energy of these waves will be transmitted through the circuit A, and the detector 26, to the selective circuits C, D; C,"D?, etc. If the received carriers differ by appropriate amounts and the selective circuits are suitably tuned, the appropriate signal will be received in each receiver 13. The receivers 13 may be listened to by a single operator or by several operators as may be desirable. Suppose the local carrier f has a frequency of500,000 cycles and the distant carriers are 520,000 cycles and 530,000 cycles respectively, then the circuits C, D" may be adjusted to select a 20,000 cycle auxiliarycarrier and the circuits C,D, a 30,000 cycle auxiliary carrier. At the distantstation which is transmitting on the 520,000 cycle principal carrier, the auxiliary carriers will be 10,000 and 20,000 cycles respectively. At the station transmitting on the 530,000 cycle principal carrier, the auxiliary carrier frequencies will be 10,000 'and 30,000 respectively. Interference from other stations will'be cutout due to the antenna' tuning and the selectivity of the auxiliary frequency carrier circuits. A combination of the arrangements of Figs. 9 and 10 maybe made by applying an auxiliary carrier'source 36fto the input of each detector 12 of Fig. 10 and I'Jlacing such circuits'asH', J of Fig- 9 and an additional detector in the output circuit of .each of the tubes 12 of Fig. 10. y

' It is not essential that a vacuum tube detector housed in carrying out the principles of this invention as any suitable detector may be utilized. The principal requirement is that the detector selected should not be overloaded. Although illustrated in connection with radio telephone systems, the invention is equally ap plicable to wire and wireless systems, and may be, applied in telegraphy.

The novel features believed to beinherent inthe invention are defined in the appended claims.

' What is claimed is 1. .The method of duplex telephony which comprises transmitting speechin one direction between two stationsby means of a carri-er. wave,,transmitting speech in the other direction by means of a carrier wave having a difl'erentfrequency, and utilizing at one of said stations a portion of the energy of the outgoing carrier Wave to produce a wave from which both of the speech signals may be derived.

2. A signal transmission system comprising two stations each. of which comprises a source of signaling waves, and a high frequency carrier source, means for combining at each of said stations the energy of each of said carrier waves to produce an intermediate trequency carrier, and means for deiving each of said signal waves from said intermediate carrier.

3. A station for duplex radio communication comprising receiving devices connected to a radiating member in approximately balanced relation with respect to sending devices, a circuit between the radiating member and the receiving devices which discriminates against the transmitted wave frequency, and means for usefully utilizing the energy from the transmitting device which is impressed upon the receiving device owing to the slight departure from the balanced relation and the imperfect selectively of said circuit.

4. A radio system comprising three or more stations each having its transmitter adjusted totransmit signals upon a carrier wave of a given frequency, means at each of said stations whereby messages may be simultaneous- 1y received from each of said other stations, said means including a different receiving circuit for the waves from each of the other stations, and means forcombining energy of the outgoing carrier wave with the incoming waves from the other stations.

5. A radio telephone system comprising three or more stationseach provided with means comprising circuits in an un *arying state ofcontinuity whereby each station may transmit on a difi'erent wave length and each may receive messages transmitted from any or all of theother stations on the wave lengths used by the other stations, and devices whereby each operator may break in merely by talking in his transmitter.

6. A wireless systemin which the transmission system comprises a radiating antenna circuit and a thermionic discharge device connected to said circuit for generating oscillations therein at the natural "frequency of said circuit, modulating means for causing said oscillations to vary in accordance with signals, and wherein a wave receiving conductor circuit of high impedance to current having the frequency of said oscillations is provided in energy transferring relation to said antenna, receiving means associated with said wave receiving circuit, said receiving means comprising detectors and selective circuits for combining energy of the incoming and outgoing carrier frequencies, and indicating means.

7. A station for communicating systems comprising means {or transmitting signaling energy, means for combining received energy with a portion of said transmitted energy, means for detecting said combined energies, means for combining wave energy of a character differing from any of said preceding energies with said detected energy, and means for detecting, selecting, and deriving a signal from said last mentioned combination of energies.

8, A station comprising a transmitting os cillator for generating waves to be trans n'iitted, a receiving conductor for conveying received Waves, means for limiting to a small value the energy produced by the transmitting oscillator received in the receiving circuit, and means for combining the energy of the received waves with the energy of the transmitted oscillator received in the receiving circuit to produce a combination frequency wave.

9. A signaling system comprising an antenna circuit, a transmitter circuit and a receiver circuit connected to said circuit, said antenna having a degree of freedom and coin sequently being resonant at a frequency of Waves to be transmitted, a path connected to said antenna for giving it another degree of freedom and consequently making itresonant at another frequency of waves to be received, reactance means in said path for changing the frequency at which said an tenna is resonant for receiving without materially varying the frequency at which said antenna is resonant for transmitting, said receiver circuit being coupled to said antenna by means whereby only a relatively small amount of energy of the transmitted frequency is received in said receiver circuit, in combination with means for combining in said receiver circuit the outgoing and incoming carrier Wave frequency energy.

10. A duplex signaling station comprising transmission and reception circuits connected to an antenna in balanced relation, and means for utilizing the small energy of the transmitted Wave which enters the receiving circuit notwithstanding the balanced relation by combining it with the energy of received waves to produce auxiliary waves, and means to detect the auxiliary waves to pro duce audible waves;

11. A radio system comprising three or more stations, each having its transn'iittcr adjusted to transmit signals on a carrier wave of frequency materially different from the Waves transmitted by the other stations, and means at each of said stations whereby the outgoing carrier Wave cooperates in enabling messages to be simultaneously received from each of the other stations.

12. The method Which comprises combining a modulated incoming carrier wave with a modulated outgoing carrier wave, producing local indications corresponding to the modulation of each of said waves and of equal intensity in case the percentage of modulation of each wave is equal to that of the other, and departing from equality of intensity in a ratio determined by the relative percentages of modulation of said Waves.

13. The method which comprises receiving an incoming wave of feeble energy, transmitting an outgoing wave of large energy, combining energy of said incoming wave with some energy of the outgoing carrier wave frequency, and producing local indications from each of said waves of intensities practically independent of the relative intensities of their combined energies.

ll. In combination with a method in accordance with claim 13, the method which comprises producing local indications of relative intensities independent of the relative intensities of the transmitted and received energies as Well as independent of the relative intensities of the locally combined energies.

15. A transmitting system comprising a source of outgoing carrier waves, a device having a characteristic over a substantial range of which it produces frequency components equal to the sum and dilference of impressed waves, means for impressing upon said device incoming wave energy and energy oi the outgoi' g carrier wave frequency, and means for preventing impression upon said device of sufficient energy of the outgoing carrier wave frequency to cause it to be overloaded, thereby preventing said device from operating beyond the range of that portion of its characteristic over which it is etiicient to produce sum and difference frequencies.

16. The methoo of two-way signaling by means of carrierwaves modulated at audible frequencies which comprises locally combining incoming and outgoing carrier waves to produce wave energy of audible frequency corresponding to the modulation of the incoming waves and wave energy of audible frequency corresponding to the modulation of the outgoing waves, and maintaining a ratio between said audible frequency wave energies which is independent of the ratio of the combined energies.

17. In combination with a method in accordance with the preceding claim, the method of maintaining the energies of audible frequency in ratio proportional to the percentage of modula ion of the carrier waves, and substantially independent of their relative amplitudes.

18. A two-way system for radio communication comprising a single aerial for radia tion and reception, transmitting means for impressing the energy of an outgoing carrier wave upon said aerial, impedance means in circuit with said aerial, a receiving circuit associated with said aerial in such relation with respect to said transmitting means to allow a la go proportion of received energy to enter said receiving circuit and but a small proportion of energy from said transi'nitting means to enter said receiving circuit, a wave distorting device in said receiving circuit, and

another Wave distorting device connected to the output circuit of said first mentioned device.

19. A system for two-way transmission comprising a continually act-ing source of Waves for transmitting outgoing signals, means for combining waves from said source with a plurality of incoming carrier waves to effect a translation of their frequencies to a different range of frequencies, and means for separately selecting the translated frequencies.

20. A system for two-way transmission comprising a continually acting means for generating outgoing carrier waves, means for combining waves from said continually acting means with a plurality of incoming waves to effect a translation of their frequencies to a materially lower range of frequencies, and means for separately selecting each of the translated frequencies.

21. In a signaling system, means for com bining incoming and outgoing carrier waves to produce an auxiliary carrier wave, in combination with means for first amplifying and then selecting the auxiliary carrier wave energy.

22. In a signaling system, means for combining incoming and outgoing carrier waves to produce an auxiliary carrier wave, in combination with a band pass filter for separating the auxiliary carrier wave from other wave components.

23. In a wireless telephone system, a pair of distantly located stations each comprising a transmitter and a receiver, each transmitter including a source of radio frequency continuous oscillations, the difference between the operating frequencies of said transmitters being a beat frequency above good audibility modulated with the speech waves of whichever of the two transmitters is modulating its outgoing wave at the particular instant, and means at each receiver for detecting and indicating with intelligible telephonic quality and volume both the signal components of said beat frequency.

24. A duplex radio telephone systemcomprising an aerial structure having two branches to ground, transmission apparatus electrically coupled to said aerial structure comprising high frequency Wave generating apparatus, modulating apparatus for modulating said waves in accordance with speech and means for impressing the generated waves upon said aerial structure, one of said branches to ground including a tuned loop circuit whereby current of the frequency generated by said wave transmitting apparatus passing through said path is regulated and reduced to small intensity, a receiver circuit connected to said one branch comprising a detector for combining energy of the frequency of the waves produced by said generating apparatus with incoming high frequency waves to produce waves of intermediate frequency, and detecting means for reproducing incoming and outgoing telephone messages from said waves of intermediate frequency.

25. A duplex radio telephone system comprising a circuit arrangement including an aerial proper and two branches to ground, one of said branches being in a path including the aerial proper which path is of low impedance for a high frequency wave of given frequency and a transmitter impressing a wave of such frequency upon said path, the other branch being in a path including the aerial proper and of relatively low impedance to a dilferent high frequency wave, said other branch including circuit elements offering high impedance to a voltage of the transmitter frequency applied across the terminals thereof, and a receiver coupled to said other branch comprising a detector for combining energy of the frequency of the waves produced by said transmitter with incoming waves to produce an auxiliary carrier wave, and means for deriving speech waves from said auxilary carrier wave.

In witness whereof, I hereunto subscribe my name this 26th day of September, A. D.

JOHN F. FARRINGTON. 

